Control of organ mass/size in plants is a significant goal in commercial agriculture. Plant shoot vegetative organs and/or structures (e.g., leaves, stems and tubers), roots, flowers and floral organs (e.g., bracts, sepals, petals, stamens, carpels, anthers), ovules (including egg and central cells), seed (including zygote, embryo, endosperm, and seed coat), fruit (the mature ovary) and seedlings are the harvested product of numerous agronomically-important crop plants. Therefore the ability to manipulate the size/mass of these organs/structures through genetic control would be an important agricultural tool.
The intrinsic plant organ size is determined genetically, although it can be altered greatly by environment signals (e.g., growth conditions). In general, larger organs consist of larger numbers of cells. Since neither cell migration nor cell death plays a major role during plant development, the number of cells in plant organs depends on cell proliferation. Precise regulation of cell proliferation is also necessary for proper development of reproductive organs that make plants fertile. While some basic research has identified genes involved in plant organ development and fertility, little is known about genetic control of cell proliferation or its link to organogenesis including organ size/mass control and fertility in plants. Therefore an important goal is to understand the connection between genes that control organogenesis and genes that control cell proliferation. A great deal of basic research has shown that the components (e.g., cyclin dependent kinases, cyclins and their inhibitors) and mechanisms (e.g., regulation by phosphorylations, ubiquitin-mediated proteolysis) that control the cell cycle in yeast and animals are conserved in higher plants (Burssens et al., Plant Physiol Biochem., 36:9-19 (1998)).
In Arabidopsis, the developing flower includes the ovule, the precursor of the seed. Wild-type ovule development in Arabidopsis has been extensively analyzed (Robinson-Beers et al., Plant Cell, 4:1237-1249 (1992); Modrusan et al., Plant Cell., 6:333-349 (1994) and Schneitz et al., Plant J., 7:731-749 (1995)). A variety of mutations that affect ovule development have been identified (Klucher et al., Plant Cell, 8:137-153 (1996); Elliott et al., Plant Cell., 8:155-168 (1996); Baker et al., Genetics., 145:1109-1124 (1997); Robinson-Beers et al., Plant Cell., 4:1237-1249 (1992); Modrusan et al., Plant Cell., 6:333-349 (1994); Ray, A., et al., Proc Natl Acad Sci USA., 91:5761-5765 (1994); Lang, et al., Genetics, 137:1101-1110 (1994); Leon-Kloosterziel, Plant Cell., 6:385-392 (1994); Gaiser et al., Plant Cell, 7:333-345 (1995)), and some of them have been found that specifically affect patterns of cell division (Schneitz et al., Development, 124:1367-1376 (1997)). Of those, several genes have been cloned; AINTEGUMENTA (ANT) (Klucher et al., Plant Cell., 8:137-153 (1996); Elliott et al., Plant Cell., 8:155-168 (1996)), AGAMOUS, (Yanofsky et al., Nature, 346:35-39 (1990); Bowman et al., Plant Cell., 3:749-758 (1991)), SUPERMAN (Sakai et al., Nature, 378:199-203 (1995)). Because these genes are expressed and function not only in developing ovules but also in various developing organs, analysis of these mutations and genes has provided general information about the control of cell proliferation during plant development.
Another trait important to the manipulation of crop species is the ability to reproduce or propagate plants through asexual means, particularly vegetative propagation of sterile or hybrid plants, and regeneration of plants from transformed cells. Asexual reproduction includes regeneration of plants from cells or tissue, propagation of plants through cutting by inducing adventitious shoots and roots, and apomixis by forming somatic embryos. Asexual reproduction has the advantage that genetic clones of plants with desirable traits can be readily produced. Although asexual propagation of plants has been applied for improving agriculture for many years, not all plants can produce adventitious shoots or roots, or regenerate whole plants from cells or tissue.
In spite of the recent progress in defining the genetic control of plant cell proliferation, little progress has been reported in the identification and analysis of genes effecting agronomically important traits such as organ mass/size, fertility, asexual reproduction, and the like through regulating cell proliferation. Characterization of such genes would allow for the genetic engineering of plants with a variety of desirable traits. The present invention addresses these and other needs.